Phospho-TRIM21 orchestrates RPA2 ubiquitination switch to promote homologous recombination and tumor radio/chemo-resistance

Abstract

RPA2, a key component of the RPA complex, is essential for single-stranded DNA (ssDNA) binding and DNA repair. However, the regulation of RPA2-ssDNA interaction and the recruitment of repair proteins following DNA damage remain incompletely understood. Our study uncovers a novel mechanism by which phosphorylated TRIM21 (Phospho-TRIM21) regulates RPA2 ubiquitination, thereby modulating homologous recombination and tumor radio/chemo-resistance. In the absence of DNA damage, TRIM21 mediates K63-linked ubiquitination of RPA2, countering K6-linked ubiquitination. Upon DNA damage, ubiquitination-modified RPA2 binds ssDNA, stabilizing the DNA structure and facilitating ATRIP/ATR recruitment. ATR subsequently phosphorylates TRIM21 at Ser41, leading to the dissociation of the TRIM21-RPA2 complex and a shift in RPA2 ubiquitination from K63 to K6 linkage. This shift maintains RPA2 ubiquitination homeostasis and stabilizes the RPA2-ATRIP complex, which is crucial for efficient homologous recombination (HR) repair and enhanced tumor radio/chemo-resistance. We also demonstrate that TRIM21 is frequently upregulated in cancers, and its depletion sensitizes cancer cells to radio/chemotherapy, suggesting its potential as a therapeutic target. This study provides novel insights into TRIM21’s role in the DNA damage response and its implications for cancer treatment.